Download Network Interconnections - Policy and Technical Issues

Interconnecting DG into Network
Distribution Systems
Presentation to the Massachusetts
DG Collaborative
Gene Shlatz
Stan Blazewicz
January 10, 2003
Background
• This work has been supported by the Massachusetts Renewable Energy Trust
and was directed by Raab Associates, Ltd (facilitator of the Massachusetts
Distributed Generation Collaborative).
• The views expressed in this presentation represent only those of Navigant
Consulting, Inc and the presenters.
• This presentation is not complete without the accompanying oral remarks.
1
Table of Contents
1
Key Terms and Definitions
2
Radial versus Network Distribution Systems
3
Network Interconnection Opportunities and Challenges
4
Approaches from Other States and Jurisdictions
5
Conclusion
2
Table of Contents
1
Key Terms and Definitions
2
Radial versus Network Distribution Systems
3
Network Interconnection Opportunities and Challenges
4
Approaches from Other States and Jurisdictions
5
Conclusion
3
Key Terms and Definitions
We have developed some key terms & definitions that should help us
in addressing network interconnection.
• Network Systems – Power delivery systems that provide highly reliable,
continuous service via alternate supplies.
• Primary Network Distribution Lines or Feeders – Higher voltage distribution lines
(4,000 volts to 35,000 volts) that deliver power to secondary grid or spot networks.
• Secondary Network Lines – Lower voltage distribution lines (208 volts to 480
volts) that distribute power to customers located on secondary grid or spot
networks.
• Network Transformers – Converts higher distribution voltages to lower voltages
used to serve secondary networks. Power (current) is intended to flow in one
direction: high to low voltage.
• Grid or Street Networks – Low voltage lines connected in a grid arrangement,
typically serving many customers over several city blocks.
4
Key Terms and Definitions
We have developed some key terms & definitions that should help us
in addressing network interconnection (continued).
• Spot Networks – Low voltage lines typically serving one large customer or highrise building in one or a few city blocks.
• Faults (Radial or Network) – Equipment failures or conditions that must be
interrupted to limit equipment damage, minimize the number of customers
interrupted and eliminate potential safety hazards to workers and public.
• Network Protectors – Devices that interrupt power when flows are from the
secondary grid into the high voltage distribution system. The protectors are
usually attached to the low voltage side of the network transformer.
• Circuit Breakers – Devices that interrupt power flows on a primary line, usually to
isolate and clear faults. Normally located in the substation, although many utilities
install reclosers on lines to limit outage exposure.
• Reverse Power Flow – When power flows from the low voltage side (secondary)
into the high side (primary) of the network transformer, thereby causing network
protectors to operate.
5
Table of Contents
1
Key Terms and Definitions
2
Radial versus Network Distribution Systems
3
Network Interconnection Opportunities and Challenges
4
Approaches from Other States and Jurisdictions
5
Conclusion
6
Radial versus Network Distribution Systems
Simplified Illustrations
Three distribution systems could be addressed in interconnection
standards and requirements.
SIMPLIFIED ILLUSTRATIONS
Radial System
Spot Network
Substation
Substation
HV
Grid Network
Substation
HV
HV
Load
TX & NP
TX & NP
Load
Load
Load
TX & NP
TX & NP
Loads designated
by arrows
Load
LV
LV
Loads
NP = Network Protector
TX = Transformer
HV = High Voltage
LV = Low Voltage
7
Radial versus Network Distribution Systems
Key Differences
In general, there are key differences between radial, spot network and grid
network distribution systems.
Issue/Description
Radial Systems
Spot Networks
Grid Networks
No. of Primary Feeders
(Typical)
1
2-4
4-8
480 volts
208 volts
Voltages
4000 volts to 35,000
volts
Locations
Urban, Suburban or
Rural
Urban and Suburban
Urban
Area Served (Typical)
Up to 30 to 40 miles. 510 miles for main feeder
One Building Complex,
High Rise or Single
Customer
Several City Blocks;
Sometimes Larger
Length of Secondary
Circuits
Typically less than 300
feet to meter.
Typically less than 100’
to customer switchgear
Individual sections can
be up to 500’ to 600’ feet
Construction Type
Overhead or
Underground
Almost Always
Underground
Almost Always
Underground
Level of reliability
Typically 1 to 3
interruptions per yr
Reliability improved by a
factor of 5-10
Reliability improved by a
factor of 5-10
Relative Cost
Base-Urban systems
typically higher than
rural/suburban
High, due to redundancy
and high cost equipment
Very high, due
redundancy and urban
location
Circuit loadings
All load served by a
single circuit
Loads balanced equally
on network transformers
Relative loadings may
vary on network
transformers
8
Table of Contents
1
Key Terms and Definitions
2
Radial versus Network Distribution Systems
3
Network Interconnection Opportunities and Challenges
4
Approaches from Other States and Jurisdictions
5
Conclusion
9
Network Interconnection Opportunities and Challenges
Attractive market opportunities for distributed generation may exist that
require network interconnection.
• Secondary networks are used in about 90% of the cities in the US having a
population of >100,000 and in more than 1/3 of the cities with populations
between 25,000 – 100,000.1
• Some of the more attractive and most accessible market opportunities for DG
involve commercial customers in urban areas:
–
–
–
–
–
Relatively high electricity prices
Reasonable gas prices, accessibility to gas
Electricity can be a significant operating cost
Customers care about costs, reliability, power quality and green attributes
Technical fit
- Right size (I.e. MW) for some DG technologies (microturbines, fuel cells and recip
engines)
- PV opportunity
- Cogen opportunity
• It would appear that many of these customers are in urban areas on grid or
spot networks.
1.
Standard Handbook for Electrical Engineers, 13th Edition, 1993
10
Network Interconnection Opportunities and Challenges
There are challenges with interconnecting DG into spot and grid networks.
• Single greatest challenge is to address the possibility that DG will cause
network protectors to open under non-fault conditions; for example,
when DG output causes reverse power flows on network protector(s).
• Whether the length of time required to analyze DG impacts is longer than radial
systems due to greater complexity of network systems, particularly on grid
networks with many primary feeders and secondary transformers.
• Development of a generic standard for integration of DG presents potential
challenges due to significant differences in network system design within and
among utilities, particularly for grid systems that have evolved over time.
• Similar to radial systems, need to ensure fault current contribution by DG does
not exceed the fault duty ratings of primary and/or secondary equipment; for
example, circuit breakers.
• If clearing times for DG exceed those of the network protectors, need to
address potential mis-coordination or de-sensitization of protection systems.
• Identifying mitigation options for synchronous generators that potentially could
remain on line and contribute fault current to primary and secondary faults.
11
Network Interconnection Opportunities and Challenges
Faults should be easily isolated on a radial feeder with DG.
Substation
Circuit Breaker
Load
Substation Circuit Breaker
Opens and DG Protection
Operates to Isolate Fault
Direction of
Fault Current
Load
DG Provider
Load
12
Network Interconnection Opportunities and Challenges
Fault protection becomes more difficult on network feeders with DG
installed.
Incoming
Transmission
Lines
Substation
Substation Circuit Breaker
Opens and Network Protector
No. 2 Opens to Isolate Fault.
Direction of
Fault Current
Potential for NP No.1 to Also
Open if Protection does Not
Properly Coordinate
NP No. 2
NP No. 1
DG Provider
Loads
NP = Network Protector
13
Network Interconnection Opportunities and Challenges
Reverse power could also be an issue for network feeders with DG
installed .
Incoming
Transmission
Lines
Substation
Potential for Either Network
Protector No.1 or No. 2 to
Open Under Reverse Power if
DG Output Exceeds Flows On
Feeder 1 or Feeder 2 (F1 or F2)
For Example, if Net DG Output
is 250kW and Either F1 or F2 is
Less Than 250kW, Then the
Network Protector Could Open
F1
NP No. 1
F2
NP No. 2
DG Provider
Loads
NP = Network Protector
F = Feeder
14
Table of Contents
1
Key Terms and Definitions
2
Radial versus Network Distribution Systems
3
Network Interconnection Opportunities and Challenges
4
Approaches from Other States and Jurisdictions
5
Conclusion
15
Approaches from Other States and Jurisdictions
Several jurisdictions have begun to address network interconnection of
DG.
• Texas – Included both spot and grid networks
• California – Dealt with in supplemental review
• FERC ANOPR – Considered in both primary and secondary screens
• IEEE – Covers spot networks only
16
Approaches from Other States and Jurisdictions
Texas-Overview
The Texas rules cover network interconnection; however, there has been
limited experience with using these rules for network interconnection.
• The Public Utility Commission of Texas Interconnection Manual provides screens for
interconnection into secondary networks.
– These screens cover:
- Equipment pre-certification
- Size of DG
· Unit size
· Relative to the feeder load
· Relative to the customer’s load
- Technology type
– If the application passes these screens, the application is approved and there is no
study fee.
– If the application fails any of the screens, the applicant is charged for a study and the
utility will make a recommendation to the applicant on how to proceed.
• The utility can always perform a study, but not always charge the customer. Regardless
of who pays for the study, the utility may reject an application for safety or reliability
issues.
• Since the standard has been in place, there has been little activity regarding network
interconnection using these rules.
17
Approaches from Other States and Jurisdictions
Texas
The Texas rules allow for simple interconnection approval and relief from
study fees for network interconnection under certain circumstances.
Proposed System on
Network Secondary
(h,i)
Equipment Precertified? (?)
No
Yes
Aggregate DG 
25% of Feeder Load?
No
(h-1, h-2)
Yes
Yes
DG < 20kW,
Inverter based?
No
(i)
Yes
Inverter-based
Protective Function ?
(h-1)
Source: Distributed Generation
Interconnection Manual, Public
Utility Commission of Texas, May
1, 2002, Figure 4-2: Network
Secondary Study Chart
No
DG < customer
minimum load?
No
(h-2)
Yes
No Study Fee Allowed
Study Fee Allowed
(g-2, m-1)
(g-2, m-1)
Approve Application
Recommendation
18
Approaches from Other States and Jurisdictions
Texas
The Texas rules allow for simple interconnection approval and relief from
study fees for network interconnection under certain circumstances
(continued).
“Certain aspects of secondary network systems create technical difficulties that may make
interconnection more costly to implement. If the proposed site is serviced by a networked secondary,
no study fee may be charged to the applicant if:
 Proposed DG equipment is pre-certified
 Aggregate DG, including the proposed system, represents 25% or less of the total load on the network
(based on the most recent peak load demand)
and either
 Proposed DG has inverter-based protective functions, or
 Proposed DG rating is less than the local applicant’s verifiable minimum load.
Otherwise, the TDU may charge the DG applicant a fee to offset the costs of the interconnection study.
The TDU must advise applicants requesting DG interconnection on secondary networks about the
potential problems and costs before initiating the study.
Note that these provisions do not preclude the TDU from performing a study; they simply regulate when
the TDU can charge the applicant for the cost of the study. Whether or not a study fee is billable to the
applicant, the TDU may reject an application for demonstrable reliability or safety issues but must work
to resolve those issues to the mutual satisfaction of the TDU and applicant. The TDU must make
reasonable efforts to interconnect all proposed DG, including the possibility of switching networksecondary service to a radial feed if practical and if acceptable to the applicant.”
Source: Distributed Generation Interconnection Manual,
Public Utility Commission of Texas, May 1, 2002
19
Approaches from Other States and Jurisdictions
Texas
Major problems have not been reported in Texas, however they have little
practical experience with the network interconnection using the rules.
• Standards have been in place since January 2001.
• No complaints have been reported to the Public Utility Commission of Texas.1
• ONCOR has processed 19 applications (2001-2002).2 This represents about
80% of all applications in Texas.
– Only one application was for a network interconnection. That project was an 8MW
(4x2MW recip engine) back-up power system installed in a 4kV spot network.
– The network interconnection aspects of the standard do not appear to be a concern
to ONCOR. The rules allow, “A utility may reject applications for a distributed
generation facility under this section if the utility can demonstrate specific reliability
or safety reasons why the distributed generation should not be interconnected at the
requested site. However, in such cases the utility shall work with the customer to
attempt to resolve such problems to their mutual satisfaction.”
• Centerpoint Energy has not received any applications for network
interconnection.3
1.
2.
3.
Telephone Interview with Tony Marciano, Public Utility Commission of Texas, Electric Division January 7, 2003
Telephone Interview with Ken Brunkenhoefer, ONCOR Electric Delivery Company January 7, 2003
Telephone Interview with Ben Gazara, Centerpoint Energy, January 8, 2003
20
Approaches from Other States and Jurisdictions
California
California’s Rule 21 does not currently deal with network interconnection
directly; it is unclear if this is a major concern.
• The first screen in the initial review process puts network interconnection into
supplemental review.
• It is It has been suggested that network interconnection may be lengthening
the time for supplemental review for some utilities. However, data is not
readily available to support that position.
• The Rule 21 Working Group is developing guidelines for supplemental review
which addresses what happens if an application fails a screen.1
– Network interconnection may be addressed in these guidelines, however
other screens (non-export screen and 15% screen)appear to be priorities.
• SCE and SDGE have not received any applications for network
interconnection.2,3,4
– SCE has processed approximately 1400 applications (1200 for PV) since
Rule 21 was established. SDG&E has processed approximately 700
applications (650 for PV).
– These utilities have limited network distribution in their systems.
1.
2.
3.
4.
Telephone Interview with Scott Tomashevsky, California Energy Commission, January 7, 2003
Telephone Interview with Tom Dossey, Southern California Edison, January 8, 2003
Telephone Interview with Mike Iammarino, San Diego Gas and Electric, January 8, 2003
Note: PG&E could not be reached. PG&E is likely to have more network distribution systems
21
Approaches from Other States and Jurisdictions
FERC
The FERC ANOPR Interconnection Procedures document addresses
networks, however the details have not been worked out.
• During the initial review the interconnection provider would apply primary and
secondary screens to determine how the application will be treated.
– If the applicant passes the primary screens the application is approved.
– If the application fails one or more primary screens but passes the
secondary screens it still may qualify for simple interconnection.
• There are primary and secondary screens that cover network interconnection.
• The details for these screens have not been worked out.
22
Approaches from Other States and Jurisdictions
FERC
The details still need to be worked out for the primary screen that
addresses network interconnection.
“4. Screening Criteria for Determining Grid Impacts
a. Primary Screening Criteria
2. For interconnection of a proposed generator to the load side of spot network protectors, the proposed
generator must utilize an inverter based equipment package and, together with the aggregated other
inverter-based generation, will not exceed the smaller of 5% of a spot network’s maximum load or 50
kW [IP POSITION: AND MUST COMPLY WITH ALL REQUIREMENTS OF IEEE P1547, SECTION
4 “INTERCONNECTION TECHNICAL SPECIFICATIONS AND REQUIREMENTS”].
3. [SGC POSITION: FOR INTERCONNECTION OF GENERATORS TO THE LOAD- SIDE OF
SECONDARY GRID NETWORKS, THE PROPOSED GENERATOR MUST BE AN INDUCTION
GENERATOR THAT DOES NOT EXCEED 50% OF THE MINIMUM LOAD OF THE HOST
FACILITY OR A GENERATOR WITH AN INVERTER-BASED EQUIPMENT PACKAGE WHICH
DOES NOT EXCEED THE GREATER OF 50% OF THE MINIMUM LOAD OF THE HOST
FACILITY OR 20 KW NOT EXCEEDING 30% OF PEAK LOAD.]
[IP/NARUC POSITION: THE PROPOSED GENERATOR CANNOT BE CONNECTED ON THE
LOAD SIDE OF A SECONDARY NETWORK PROTECTOR, EXCEPT AS ALLOWED UNDER
SECTION 4.a.2 (SPOT NETWORK) ABOVE.]”
Source: Report to FERC on Standardization of Small Generation Interconnection Agreements and Procedures, November 12, 2002
Note:
SGC POSITION - Small Generator
IP POSITION - Interconnection Provider
NARUC POSITION - National Association of Regulatory Utility Commissioners
23
Approaches from Other States and Jurisdictions
FERC
The details still need to be worked out for the secondary screen that
addresses network interconnection.
“4. Screening Criteria for Determining Grid Impacts
a. Secondary Screening Criteria
2. [SGC POSITION: FOR INTERCONNECTION OF A PROPOSED GENERATOR TO A SPOT NETWORK CIRCUIT,
THE NEW UNIT IN AGGREGATE WITH OTHER GENERATION WILL NOT EXCEED 5% OF THE SPOT
NETWORK’S MAXIMUM LOAD.] [IP/NARUC POSITION: FOR INTERCONNECTION OF A PROPOSED
GENERATOR TO THE LOAD SIDE OF SPOT NETWORK PROTECTORS, THE PROPOSED GENERATOR MUST
UTILIZE AN INVERTER BASED EQUIPMENT PACKAGE AND, TOGETHER WITH THE AGGREGATED OTHER
INVERTER-BASED GENERATION, WILL NOT EXCEED THE SMALLER OF 5% OF A SPOT NETWORK’S
MAXIMUM LOAD OR 50 KW AND MUST COMPLY WITH ALL REQUIREMENTS OF IEEE P1547’S
“INTERCONNECTION TECHNICAL SPECIFICATIONS AND REQUIREMENTS”.]
3. For the interconnection of a proposed generator to any network, the generator [SGC POSITION: WILL EITHER
UTILIZE] [IP/NARUC POSITION: MUST UTILIZE A PROTECTIVE SCHEME THAT WILL ENSURE THAT ITS
CURRENT FLOW WILL NOT AFFECT THE NETWORK PROTECTIVE DEVICES INCLUDING] reverse power
relays or a comparable function [SGC POSITION: TO ENSURE THAT ITS CURRENT FLOWS CANNOT AFFECT
NETWORK PROTECTIVE DEVICES]. [IP/NARUC POSITION: SYNCHRONOUS GENERATORS CANNOT BE
INTERCONNECTEDINTO A SECONDARY NETWORK.]
4. [SGC POSITION: NOTWITHSTANDING SUBSECTION B. 3, FOR INTERCONNECTION OF A PROPOSED
GENERATOR TO A SECONDARY GRID NETWORK WHOSE TOTAL NET GENERATING CAPACITY, IN
AGGREGATE WITH OTHER EXPORTING GENERATORS INTERCONNECTED ON THE LOAD SIDE OF
NETWORK PROTECTIVE DEVICES, WILL NOT EXCEED THE LESSER OF 10% OF THE MINIMUM ANNUAL
LOAD ON THE NETWORK OR 500 KW.] [NARUC/IP POSITION: FOR INTERCONNECTION OF A PROPOSED
GENERATOR THAT IS AN INDUCTION GENERATOR OR THAT UTILIZES INVERTER BASED PROTECTIVE
FUNCTIONS, BOTH OF WHICH INCLUDE REVERSE POWER RELAY FUNCTIONS, THE GENERATOR’S TOTAL
NET GENERATING CAPACITY, IN AGGREGATE WITH OTHER GENERATORS INTERCONNECTED ON THE
LOAD SIDE OF NETWORK PROTECTIVE DEVICES, DOES NOT EXCEED THE LESSER OF 10% OF THE
MINIMUM LOAD ON THE NETWORK OR 50 KW. A SMALL GENERATOR DOES NOT EXPORT TO ANY
NETWORK.] “
Source: Report to FERC on Standardization of Small Generation Interconnection Agreements and Procedures, November 12, 2002
24
Approaches from Other States and Jurisdictions
IEEE
IEEE 1547 will provide little guidance on network interconnection outside of
spot networks.
• IEEE 1547 only covers spot networks, secondary grid networks may be
included in future revisions.
• IEEE 1547.2 is a guidebook that is under development and may cover network
interconnection.
“4.1.4.2 Distribution Secondary Spot Networks 3
Network protectors shall not be used to separate, switch, serve as breaker failure backup or in any manner isolate a
network or network primary feeder to which DR is connected from the remainder of the Area EPS, unless the protectors
are rated and tested per applicable standards for such an application.
Any DR installation connected to a spot network shall not cause operation or prevent reclosing of any network protectors
installed on the spot network. This coordination shall be accomplished without requiring any changes to prevailing
network protector clearing time practices of the Area EPS.
Connection of the DR to the Area EPS is only permitted if the Area EPS network bus is already energized by more than
50% of the installed network protectors.
The DR output shall not cause any cycling of network protectors.
The network equipment loading and fault interrupting capacity shall not be exceeded with the addition of DR.
DR installations on a spot network, using an automatic transfer scheme in which load is transferred between the DR and
the EPS in a momentary make-before-break operation, shall meet all the requirements of this clause regardless of the
duration of parallel.
3 When
required by the authority who has jurisdiction over the DR interconnection, a study may be conducted to determine that all of the requirements of this
clause canSource:
be met when
aggregate
DR installed on a spot network exceeds 5% of the spot network’s maximum load.”
IEEEthe
1547,
Draft 10
25
Table of Contents
1
Key Terms and Definitions
2
Radial versus Network Distribution Systems
3
Network Interconnection Opportunities and Challenges
4
Approaches from Other States and Jurisdictions
5
Conclusion
26
Conclusion
Conclusion
• We have established key definitions and a framework for thinking about
network interconnection.
• There are opportunities and challenges for network interconnection.
• Other jurisdictions have done work on establishing standards and rules for
network interconnection, however there is little practical experience with these
standards.
27
Conclusion
Defining the scope of the Collaborative’s work on developing network
interconnection standards
• What can the Collaborative leverage from the radial work?
– Timelines
– Fees
– Process flow diagram
• Are there other parts that should be similar to radial?
– Agreements
– ADR
• Can the Collaborative address spot networks by the end of February?
• Can the Collaborative address grid networks by the end of February?
• Can the Collaborative use screens for network interconnection?
• Can the Collaborative use Texas or the ANOPR as a starting point?
28